Quality control facilities for large optical reflectors at ENEA-
Casaccia for physics application
Stefania Baccaro a,d, Carlo Bosio b,d, Augusto Maccari c, Marco Montecchi a,d
a) ENEA FIS-ION, Casaccia, Roma, Italyb) Dipartimento di Fisica Università La Sapienza, Roma, Italy
c) ENEA SOLTERM, Casaccia, Roma, Italyd ) INFN – Sezione di Roma1, Roma, Italy
Large optical reflectors are used in…
• Astronomy: in telescope (imaging)
• High Energy Physics: in RICH, to focus Cherenkov radiations on optical sensor (quasi-imaging)
• ……
• Solar Energy: as sun-power collectors (collecting)
… for information completeness
• How large? Single panel, up to some meters
• Imaging use is much more demanding than collecting one
• Composition and shape are designed for the specific application and .....
... HAVE TO BE TESTED !!!
Irradiation plants at ENEA – Casaccia
• TAPIRO: fast neutrons• TRIGA: thermal neutrons• CALLIOPE: 1.17 and 1.33 MeV
Optical laboratory tender to Calliope: spectrophotometers and spectrometer Light-Yield damped optical top with light sources, lenses,
mirrors, detectors, etc.. custom set-up
Optical tests at ENEA-Casaccia
spectrophotometer – specular and diffused (small flat sample)
spectrometer – specular (full scale reflector)
2f optical test focal length and image spot dimension
pin-hole optical test visual inspection of the curvature
profilometer accurate measurement of the curvature
Shape performances:
Reflectance:
2f optical test:focal length and image-spot dimension
2 f
screen
image
LED ( = 5 mm)
in the ideal case, image and source have the same dimension
Pin-hole optical test:a visual inspection of the curvature
where the surface image is dark, the curvature is wrong
surfaceimage
2 f
LED
pin-hole f1
p q
LHCb RICH mock-up: carbon fiber + honeycomb
~ 600 mm 2f = 1700 20 mm
image spot ~ 15 mm
LHCb mock-up : polymethylmethacrylate (PMMA) hot bended and honeycomb
~ 400 mm 2f = 2370 20 mm
image spot ~ 25 mm
LHCb RICH mock-up:PMMA poured liquid on master
~ 350 mm 2f = 2330 20 mm
LHCb mock-up: electrodeposited Ni
= 200 mm 2f = 315 5 mm
Accurate test of the reflector curvature: profilometer
In the framework of the Concentrating Solar Power Project, ENEA is providing with an optical profilometer to test large linear parabolic reflectors
the measurement is automatic - PC controlled
the profilometer can be used also for reflectors differently shaped (e.g. spherical reflector)
actually the instrument performs 1D scanning
2D upgrade is imminent
ENEA optical profilometer (1D)
x
HeNe
screen
y
x0xS(xC,yC)
yS
Nikon D1X, 4.024 x 1.324 px
rotation axis
• the surface is scanned by tilting the incident beam () with a high precision rotation stage (20 rad repeatability)
• the intersection of the reflected beam with the screen (XS) is deduced by processing the digital image
Data processing – 1th method: fit
N
j S
jSS
M xErr
xxppMF
1
2expsim
1,..,
x
y
x0xS simulated
xS experimental
yS
y = f (x,p1,..,pM)
y = tg() (x - x0)
best fit by minimising
Data processing - 2nd method:iterative extrapolation (I.E.)
the next point P2 is: along the incident beam, by definition in AB, if 1; P1C, P2C P1P2
univocally determined by assuming:
yS
central point ( = 90°):
(xc,yc) directly measured
set dy/dx = 0 by tilting
x
y
x0
AB
P1
P2
C
P1
P2
C
circular:P1C =CP2
P1
P2
x1 x2xC
y = x2 parabolic:
xC = (x1+x2)/2
Example: reduced scale linear parabolic reflector (aperture 0.6 m)
60 70 80 90 100 110 12022
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
rotational measurement
XS (
cm)
(deg)
experimental best fit of 32/49 data
best fit parameters:
2 = 1.23 (32/49 data)
P4 = 0.32 0.04
= 11.3 0.8 deg
f = 185.5 0.5 mm
22
424 22)1(
4 ffP
f
P
high precision
comparison of the two methods
I.E. method gives a realistic profile of the reflector
I.E. method allows to evaluate the locale deviations from the project specifications of both profile and slope
-20 -10 0 10 20
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1profile
Y (
cm)
X (cm)
best fit extrapolation
-20 -10 0 10 20-40
-30
-20
-10
0
10
20
30
40slope
atan
(dY
/dx)
(de
g)X (cm)
best fit extrapolation
validation of the iterative extrapolation method
direct measurement
-20 -10 0 10 20-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
profile deviation from circle r = 376mm
rad
ial d
evi
atio
ns
(mm
)
X (cm)
comparator iterative extrapolation
comparator
rotation stage
harm
reflector
Conclusions
The ENEA-Casaccia facilities allow to measure the most important features of large optical reflectors:
specular and hemispherical reflectance focal length surface profile
2D upgrade of the profilometer is imminent